The present invention is directed to an improved gripper assembly for a strapping machine strapping head. More particularly, the present invention is directed to a gripper assembly for use in a strapping machine head that uses a single pin and a single spring stack for effecting proper strap grip for strap tensioning and welding.
Strapping machines are in widespread use for securing straps around loads. One type of known strapper includes a strapping head and drive mechanism mounted within a frame. A chute is mounted to the frame, through which the strapping material is fed.
In a typical stationary strapper, the chute is mounted at about a work surface, and the strapping head is mounted to a horizontal or vertical portion (or perhaps an inclined portion) of the chute. The strapping or sealing head provides a number of functions. First, the strapping head includes a plurality of grippers for gripping the strap during the course of a strapping operation. The strapping head also includes a cutter to cut the strap from a strap source or supply. Last, the strapping head includes a sealer to seal an overlying course of strapping material onto itself. This seal is commonly referred to as a weld and is effected by heating overlying courses of the strap by use of a vibrating element.
In the course of the strapping operation, a first course of strapping material (e.g., the leading end of the strapping material) is conveyed from a dispenser into a feed arrangement and into the strapping head. The leading end is conveyed through the strapping head (in proximity to a first or loop gripper), through the chute, and back to the strapping head. The leading end is conveyed in the strapping head over a second or end gripper to a position within the sealing region.
The leading end is then gripped by the end gripper and the strapping material is tensioned around the load. Subsequent to tensioning, the trailing end of the strapping material is gripper by the loop gripper and the seal or weld is effected in the strap. The strap is then cut from the source or supply and is released from the strapping machine.
It is important that the grippers maintain a firm and sure grip on the strap at all “gripping” times. To this end, known strapping machines use a cam that contacts a gripper assembly to effect this grip of the strap. Known gripper assemblies include a roller (for contact with the machine camming surface) mounted to a cam follower block by a pin. A grip is rigidly mounted to a grip support which is in turn mounted to the cam follower by a second pin. A pair of side-by-side spring sets are positioned between the cam follower and the grip support to permit the grip to apply a balanced pressure to strap.
In such an arrangement, two pins are needed (one for mounting the roller to the cam follower block and a second for mounting the grip support to the cam follower block. Moreover, side-by-side sets of springs are needed to provide proper application and alignment when applying pressure to the strap (e.g., during spring compression).
While such an arrangement functions well, it does have its drawbacks. One such drawback is the complexity of the design. The need for multiple pins and multiple spring sets requires additional moving parts and components which, in mechanical systems generally is undesirable. In addition, the need for multiple pins and side-by-sides spring sets increases the overall size and thus the weight of the gripper.
Accordingly, there exists a need for a gripper assembly for a strapping machine strapping head that reduces the overall size and weight of the gripper. Desirably, such a gripper uses a reduced number of components thus resulting in a simpler, less complex gripper configuration while maintaining gripper components aligned during gripping operation.